The unusual reproductive physiology of the nematode Caenorhabditis elegans makes it an excellent model system in which to study the cell-cell interactions that occur during fertilization. Through a simple but powerful genetic screen, worms with defects in spermatogenesis or sperm function, but with no somatic abnormalities, can be isolated and maintained. This is not possible with any other commonly employed model organism, which all rely on a strictly dioecious mode of reproduction. The focus of this proposal is proteins involved in sperm-egg recognition during fertilization. A number of mutants (spe-9, fer-14, spe-13) produce cytologically normal spermatozoa, which cannot fertilize oocytes, spe-9 encodes a protein thought to function as a sperm surface ligand. Identification, cloning and analysis of genes for which mutants phenocopy spe-9 should reveal other members of the spe-9 signal transduction pathway or alternate pathways performing a similar function, which will aid in our understanding of sperm-egg communication during fertilization and cell-cell signaling in general. To accomplish this goal, the following specific aims are proposed: 1) to clone fer-14 through a combination of SNP mapping, transgenic rescue, deficiency endpoint mapping and / or a candidate gene approach; 2) to determine the rolefer-14 plays during C. elegans fertilization by examining an allellic series of mutants, the cloned sequence and the encoded protein; (3) to identify, phenotypically characterize and map new Spe mutants from the lab's collection that phenocopy spe-9, spe-13 and fer-14.